As is known in the art, frequency-hopping spread spectrum (FHSS) refers to techniques for transmitting radio signals by rapidly switching a carrier signal among many frequency channels, using a pseudorandom sequence known to both transmitter and receiver. It is used as a multiple access method in the frequency-hopping code division multiple access (FH-CDMA) scheme. Frequency-hopping signals are resistant to narrowband interference, difficult to intercept, and can share a frequency band with many types of conventional transmissions with minimal interference.
One of the challenges of frequency-hopping systems is synchronization between a transmitter and a receiver, also referred to as “time acquisition.” One known approach is to have a guarantee that the transmitter will utilize a predetermined set of channels in a fixed period of time. The receiver can then synchronize with the transmitter by picking a random channel and listening for a so-called “synchronization hop” (or “sync hop”) on that channel. Sync hops, which may be transmitted periodically, comprise known data patterns unlikely to occur within regular data transmitted on the channel.
In existing FHSS systems, time uncertainty may be resolved by selecting a time hypothesis, calculating the frequency that would be in use at that time, and then dwelling at that frequency for some interval while searching a sync hop. This process can take ten seconds or even longer.